Hearing impaired persons fitted with hearing aids, as well as persons around them, are familiar with loud, unpleasant, and often uncomfortable, screeching noises that often eminate from a hearing aid when it is turned on, and at other times as well. Persons with normal hearing have experienced similar problems with public address systems. In both hearing aids and public address systems, hereinafter referred to as communication systems of the type described, which are used in acoustic environments, acoustic feedback is the culprit. That is to say, some of the acoustic energy radiated from the speaker of a communication system into the acoustic environment is picked up by the microphone of that same system, is amplified by the system's electronics, and then rebroadcast into the environment. Under some conditions, signal reinforcement, or bootstrapping, occurs; and the result is a screeching noise that is both loud, physically uncomfortable, and annoying to all those in the vicinity of the speaker.
Screeching noise caused by acoustic feedback is a major irritation to hearing aid users as well as to persons with unimpaired hearing in their vicinity, and to persons in the vicinity of a malfunctioning public address system. Conventionally, the user of a hearing aid controls screech caused by acoustic feedback by reducing the gain on the amplifier in the hearing aid, but this expedient solves the problem at the expense of a reduction in the level of amplification of information, which is the basis for wearing a hearing aid in the first place. In addition, manual adjustment of the volume of a relatively small hearing aid is usually difficult, or at least inconvenient. In public address systems, on the other hand, resort to rearranging the microphone is often the only practical way to alleviate screeching noise. Thus, the elimination of screeching noise in a communication system caused by acoustic feedback often requires manual intercession into the operation of such system which may be inconvenient or inappropriate. Apparatus that automatically, and adaptively, overcomes the problem of screeching noise caused by acoustic feedback would therefore be very desirable.
It is an object of the present invention to provide both a method of and apparatus for automatically and adaptively overcoming the problem of screeching noise caused by acoustic feedback in a communication system of the type described.